Conventional microcapsules have been developed in the USA. There is no standard for the size of microcapsules, and the microcapsules are manufactured by injecting liquid, solid or gas molecules into minute capsules (cells) and then sealing the capsules. Depending on manufacturing methods, the microcapsules may have a diameter of several nm to mm. Further, the microcapsules can be applied to various fields, such as medicine, food, energy, agriculture and so on.
Recently, the microcapsules have also been applied to flat panel displays. In particular, a microcapsule-type electrophoretic display is considered to be a leading technical field for implementing e-paper. In the microcapsule-type electrophoretic display, several million white and black particles are injected into a microcapsule having a size corresponding to the diameter of a human hair, and microcapsules having the white-and-black particle suspensions injected therein are injected between a transparent electrode and a driving electrode.
When a negative electric field is applied to the electrophoretic display constructed in such a manner, white particles, among the suspended white-and-black particles injected into the microcapsule, are charged with positive electricity to move to the upper portion of the microcapsule. That is, the white particles crowd to one direction of the microcapsule. As such, when the white particles move to the upper portion of the microcapsule, this portion represents a ‘white color’ on the e-paper. Simultaneously, black particles crowd to the opposite side of the microcapsule such that a ‘black color’ is not represented on the surface of the microcapsule. On the contrary, in order to display a block character or picture, the opposite electric field is applied. When the opposite electric field is applied, the black particles come to the surface of the microcapsule, and the white particles are hidden from the surface.
In the above-described microcapsule-type electrophoretic display, even when power is turned off, particles do not disappear but remain on the screen. Unlike other displays, a backlight is not needed so that operating voltage is considerably reduced. Further, the contrast between white and black particles is so strong that a clear image can be seen from any angle. However, despite the above-described advantages, only black-and-white e-paper is commonly used, and the utilization range thereof is considerably limited.
To overcome such a disadvantage, attempts are being made to develop color e-paper. A method used for the development of color e-paper is where a color filter is adopted and attached to a display unit of the black-and-white e-paper so as to implement color e-paper through the same method as an LCD display. It is known that the method is being attempted by E-Ink, Inc. Further, a method of directly patterning microcapsules is being attempted. In this method, hydrophile treatment and hydrophobic treatment are performed on an electrode surface by using a hydrophilic binder surrounding microcapsules such that the microcapsules crowd to the hydrophilic surface. Attempts to form desired capsule patterns are being made. Meanwhile, methods of directly depositing microcapsules onto an electrode through electro deposition are also being attempted.
In general, binary-system materials such as microcapsules are applied in a bulk state, without attempting to form patterns in a predetermined shape. This is because inner materials should be protected or the discharge of the inner materials with functionality should be adjusted. However, when pixels are desired to be represented by capsules as in a display, respective color pixels should be arranged. When such pixels are represented by microcapsules, the microcapsules may be directly patterned and implemented as pixels. Alternately, after the microcapsules are applied in a bulk state, a color filter may then be attached. When the color filter is attached to the microcapsule layer, the electrophoretic microcapsule-type e-paper is a reflective display which does not have a backlight, unlike an LCD display. In the microcapsule-type electrophoretic e-paper, while incident light is reflected so as to pass through a microcapsule layer, a loss occurs. After that, the light passes through the color filter. Therefore, it is difficult to obtain clear color.